function [ out ] = contornos( inp )

    out = inp; %reservamos la memoria de la salida
    [heigh, width] = size(inp);
    out(2:1:heigh-1, 2:1:width-1) = ...   
                      (+1)* inp(1:1:heigh-2, 1:1:width-2) + ... % [-1,-1]
                      (+1)* inp(1:1:heigh-2, 2:1:width-1) + ... % [-1, 0]
                      (+1)* inp(1:1:heigh-2, 3:1:width-0) + ... % [-1,+1]
                      (+1)* inp(2:1:heigh-1, 1:1:width-2) + ... % [ 0,-1]
                      (-8)* inp(2:1:heigh-1, 2:1:width-1) + ... % [ 0, 0]
                      (+1)* inp(2:1:heigh-1, 3:1:width-0) + ... % [ 0,+1]
                      (+1)* inp(3:1:heigh-0, 1:1:width-2) + ... % [+1,-1]
                      (+1)* inp(3:1:heigh-0, 2:1:width-1) + ... % [+1, 0]
                      (+1)* inp(3:1:heigh-0, 3:1:width-0);      % [+1,+1]
end

